The present invention relates to a process and an apparatus for manufacturing ceramic packages for semiconductor elements such as IC chips (hereinafter referred to as ceramic semiconductor packages). More particularly, the present invention is concerned with a process and an apparatus for manufacturing ceramic semiconductor packages which comprise a lead frame having registering (guiding) holes and a ceramic substrate having a thermally fusible bonding material such as a resin or glass applied to the sealing surface of the substrate. The process and apparatus are capable of improving the positioning accuracy of the lead frame and the substrate when they are bonded together by heating to fuse the bonding material.
In recent years, there has been a tendency for the number of leads to increase in square or rectangular ceramic semiconductor packages having leads extending from all four sides such as CQFP's (ceramic quad flat packages). This tendency is accompanied by a growing demand for positioning accuracy in wire bonding in which a semiconductor chip is electrically connected to a lead frame by bonding wires usually made of aluminum or gold. This demand, in turn, requires an improvement in the accuracy of positioning when the lead frame is bonded to a ceramic substrate to manufacture a ceramic semiconductor package.
The positioning of a lead frame and a ceramic substrate has usually been performed, as shown in FIG. 6, by using a positioning jig g made of stainless steel. The positioning jig g has a recess b at the center of the jig for receiving a ceramic substrate a, and positioning pins f projecting upwards at the periphery of the jig so as to go through registering holes e formed in the peripheral tie bar portions d of a lead frame c.
Before the lead frame c is bonded to the ceramic substrate a by using the positioning jig g, a thermally fusible bonding material i such as a sealing glass is applied to the sealing surface h of the substrate a by means of screen printing, for example. Thereafter, the substrate a is placed into the recess b of the positioning jig g with the sealing surface h facing up, and the lead frame c is put on the bonding material i applied to the sealing surface h of the substrate a while achieving positioning by passing the positioning pins f of the jig g through the registering holes e of the lead frame c. Subsequently, the substrate a and the lead frame c anchored to the jig g are heated at a temperature above the fusing (melting) temperature of the bonding material i (about 350.degree. to 500.degree. C. when the bonding material is a sealing glass) to fuse the bonding material i, thereby performing bonding by causing the lead frame c to settle down onto the fused bonding material i.
However, the manufacture of ceramic semiconductor packages by bonding a lead frame and a ceramic substrate using the above-described positioning jig suffers from the following problems.
1) The positioning jig can be used interchangeably for the manufacture of packages having different designs only when the substrates a have the same outer dimensions and the lead frames c to be bonded to the substrate a have registering holes with the same dimensions at the same positions. Therefore, as a practical matter, different positioning jigs made of stainless steel must be provided for the manufacture of ceramic semiconductor packages having different designs. As a result, in the manufacture of limited numbers of a wide variety of packages, the manufacturing costs are increased and the manufacturing period is prolonged. PA1 2) Positioning is performed by placing the lead frame c on the substrate a which is received in the recess b of the positioning jig g. Due to the light weight of the lead frame c placed on the substrate a, misregister tends to occur by displacement of the lead frame c when the substrate a and the lead frame c are bonded together. PA1 3) The dimensions of the ceramic substrate a fluctuate due to firing shrinkage in the course of a process for preparation thereof. Therefore, each horizontal dimension (y.sub.1) of the recess b of the positioning jig g, in which the substrate a is received, must be determined so as to allow for both maximum deviation (.+-..delta.x.sub.1) from the corresponding horizontal nominal dimension of the substrate (x.sub.1) and maximum tolerance of finished dimension (.+-..delta.x.sub.1) of the recess b. Thus, the dimension y.sub.1 of the recess is set so as to equal the sum of x.sub.1 +.delta.x.sub.1 +.delta.y.sub.1. As a result, the horizontal position of the substrate a received in the recess b has a maximum deviation equal to (.delta.x.sub.1 +.delta.y.sub.1)/2. PA1 4) The positioning jig g must be fabricated so as to allow for the tolerances of the finished dimensions (.delta.y.sub.2, .delta.y.sub.3, and .delta.z.sub.1) of the diameter of the positioning pins (y.sub.2), the distance between the positioning pins (y.sub.3), and the diameter of registering holes (z.sub.1) formed in the lead frame, respectively. PA1 providing a lead frame-supporting plate having pin-receiving holes for registration in positions matched to the positions of the registering holes of the lead frames when the lead frames are positioned on the supporting plate; PA1 providing a positioning base beneath the lead frame-supporting plate, the positioning base having positioning pins at the same intervals as the registering holes of the lead frames; PA1 lifting the positioning base until the positioning pins of the base pass through the pin-receiving holes of the lead frame-supporting plate and protrude therefrom; PA1 positioning the lead frames or lead frame train on the lead frame-supporting plate such that the positioning pins of the positioning base, which protrude from the plate, pass through the registering holes of the lead frames; PA1 centering and positioning each of the ceramic substrates, with its sealing surface facing down, on the inner lead portion of each lead frame on the lead frame-supporting plate, the positioning being performed in such a manner that the center of the substrate coincides with that of the lead frame; and PA1 lowering the positioning base until the positioning pins of the base are withdrawn from the registering holes of the lead frames and from the pin-receiving holes of the lead frame-supporting plate. PA1 a lead frame-supporting plate having pin-receiving holes for registration in positions matched to the positions of the registering holes of the lead frames when the lead frames are positioned on the supporting plate; PA1 a vertically movable positioning base beneath the lead-frame-supporting plate, the positioning base having positioning pins at the same intervals as the registering holes of the lead frames; PA1 means for vertically moving the positioning base to allow the positioning pins of the base to pass through the pin-receiving holes of the plate and protrude therefrom; PA1 means for positioning the lead frames or lead frame train on the lead frame-supporting plate such that the positioning pins of the positioning base, which protrude from the lead frame-supporting plate, pass through the registering holes of the lead frames; and PA1 means for centering and positioning the ceramic substrates, the means capable of centering a ceramic substrate and then positioning it, with its sealing surface facing down, on the inner lead portion of each lead frame on the lead frame-supporting plate in such a manner that the center of the substrate coincides with that of the lead frame.
Of these dimensional accuracies or tolerances, the accuracy of the substrate a (.+-..delta.x.sub.1) has the largest value: is the major factor which influences positional deviation between the substrate and lead frame. As shown in Table 1 below, the dimensional accuracy of the substrate a is from .+-.0.15 mm to .+-.0.25 mm, while the accuracies or tolerances of the other dimensions are on the order of .+-.0.05 mm.
TABLE 1 ______________________________________ Dimension Accuracy or Tolerance Influence ______________________________________ Substrate, x.sub.1 .+-..delta.x.sub.1 = .+-.0.15 - 0.25 mm Maximum Jig, y.sub.1 .+-..delta.y.sub.1 = .+-.0.05 mm Moderate Jig, y.sub.1 .+-..delta.y.sub.2 = .+-.0.05 mm Moderate Jig, y.sub.1 .+-..delta.y.sub.3 = +0.05 mm Moderate Lead frame, z.sub.1 .+-..delta.z.sub.1 = .+-.0.05 mm Minimum Overall accuracy: .+-.0.18 - 0.27 mm ______________________________________
As long as the above-described positioning jig is used, the substrate must be initially positioned in the recess of the jig before the lead frame is positioned on the substrate. In this case, the large dimensional accuracy of the substrate must always be taken in to consideration when designing the jig.